mongo aggregation $group code example
Example 1: mongodb aggregate group
#equivalent of the following SQL instruction:
# SELECT COUNT(*) FROM Table
# GROUP BY your_field
query = db.collection.aggregate([
{
"$group": {
"_id": "$your_field", #GROUP BY your_field
"total": {"$sum":1} #COUNT(*)
}
}
])
Example 2: group by mongo
db.books.aggregate([
// First Stage
{
$group : { _id : "$author", books: { $push: "$$ROOT" } }
},
// Second Stage
{
$addFields:
{
totalCopies : { $sum: "$books.copies" }
}
}
])